Custom Marine (CMI)

Big Tube FF Gasket (Sold Each)

4-5/8" ID
5-13/16" OD

Big Tube Rope Seal Clamp Assembly Kit

• (1) Jumper Hose 1.25" ID
• (2) Stainless Steel Hose Clamp #24
• (1) Big Tube V-Band Clamp
• (1) 1/4-20 x 3.5" Hex Screw
• (1) Rope Seal, High Temp
• (1) Bridge Spacer, for 4.5" ID Tailpipe

Big Tube/Big E-Top Clamp & Gasket Kit

• (1) Jumper Hose 1.375" ID, 180 Degree
• (2) Stainless Steel Hose Clamp #24
• (1) Big Tube V-Band Clamp
• (1) Big Tube Flex Flare Gasket
  

How to measure riser height

Direct Mercruiser replacement for your 496 Mag or 496 HO engine. 8-1/2" Stock Riser Height. Polished. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system.

• 1 7/8" id primary to get peak horse power and torque.
• Mandrel bent and formed from High quality 316L grade material.
• Fully post annealed to reduce stresses built up in the header during the manufacturing process
• Seamless water jacketed header. No welded inner primaries or water jacketed tubes to crack and leak.
• More water jacketed protection than your stock exhaust.
• Approved by Mercruiser to not void warranty on the motor, with the exception of water reversion.
• Same high quality semi automated welding as used on all racing applications
• Cool collar patented flange design to eliminate the risk of getting water in the motor by the head flange
• This kit is price competitive to other aluminum/stainless manifold systems with superior performance and extended life span in harsh marine environments.
• No cast parts to crack, all CMI collectors are forged from American made stainless steel.
• Works on 34.5" drive centers
• Brings a race look to your stock engine.
• Sophisticated engineering leaves your stock oil lines in place and only requires relocating your oil filter with a supplied bracket.
• Step by step, do it yourself instructions using Mercury supplied engine schematics.
• Exhaust Water Temperature Bungs Installed as Standard Equipment.

The CMI 496 Sport Tube Performance Package delivers improved performance across the entire operating range of any 496 engine package. When applied to a stock 496 engine, this package will help to increase horsepower, boost mid-range torque, improve fuel economy across the power curve and enhance the engine's overall running quality. The package comes complete with all required mounting hardware plus CMI's exclusive 496 Relocation Kit, which includes all brackets, hoses and hardware needed to make relocation of select engine components easier.

Note: This CMI Systems is sold without Tailpipes

The CMI 496 Sport Tube Performance Package delivers improved performance across the entire operating range of any 496 engine package. When applied to a stock 496 engine, this package will help to increase horsepower, boost mid-range torque, improve fuel economy across the power curve and enhance the engine's overall running quality.

Note: This CMI Systems is sold without Tailpipes or Hardware. These are replacement headers only.

CMI Big Block Chevy E-Top Platinum Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for stan¬dard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Platinum Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for stan¬dard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

This Kit includes an upgrade to a Stainless Steel Water Distribution Tree.

Note: All CMI Systems are sold without Tailpipes

The all polished 3″ taller CMI Sport Tubes are a superior long tube header designed for both racing or virtually any high-performance application. For big-block applications where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines that generate more than one horsepower per cubic inch of displacement. These particular headers are commonly used in staggered forward engine applications.

The all polished 3″ taller CMI Sport Tubes are a superior long tube header designed for both racing or virtually any high-performance application. For big-block applications where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines that generate more than one horsepower per cubic inch of displacement. These particular headers are commonly used in staggered forward engine applications. Leaned for Staggered engine applications.

CMI Fusion Integrated Tailpipe Big Block Chevy Exhaust System

This is the all new, salt water rated "Fusion" Performance Header system from CMI. For years Custom Marine has produced custom exhaust systems for just about every Hi-Performance application.  But now CMI has set their sights on offering an affordable Performance Header system for the entry level Hi-Performance market with the new "Fusion" header system. This new header was designed as an affordable upgrade to exhaust manifold systems for engines needing to support upwards of 600 horsepower, while using standard Mercury Bravo exhaust exit locations. These headers are offered in the "Platinum" series finish which features a brushed satin lower section,  then mating it to a highly polished top tailpipe to produce a striking appearance on any engine. By integrating the tailpipe CMI can reduce costs to the user and eliminate costly clamps and gaskets. Premium 316L stainless steel construction, as well as the patented cool collar exhaust flange make for a durable header that will offer years of trouble free service. While the standard version is designed to fit stock Mercruiser Bravo exhaust exit locations, there are also two custom fit tailpipe options available that will allow the header to be assembled at the factory to your boats specifications. Up to a 2" vertical and/or horizontal correction can be made from the stock locations which allows this header to fit a huge range of options. (Additional charges apply)

Note: This system does not have separate tailpipes. It's pipes are set up for standard Bravo hole locations.

CMI's Gen-X Headers are the true direct factory replacement for Mercury Racing HP525EFI, HP600SCi and HP700SCi engines.

These are sold as a "pair of headers". They have the welded stainless water distribution lines like the factory OEM headers.

The new design increases water fill keeping the headers full at all time, creating cooler temperatures, which leads to improved longevity and a little extra horsepower.

Featuring more equalized primaries for improved performance, the straight-back headers with downturn collectors work with existing tailpipes and are easy to install. Constructed of quality 316L domestic stainless steel makes for one tough header with a sleek stylish look.

CMI's Gen-X Headers are a factory replacement for Mercury Racing HP525EFI, HP600SCi and HP700SCi engines. 

These are sold as a "pair of headers". This model has rubber water distribution trees for a more economical header package.

The new design increases water fill keeping the headers full at all time, creating cooler temperatures, which leads to improved longevity and a little extra horsepower.

Featuring more equalized primaries for improved performance, the straight-back headers with downturn collectors work with existing tailpipes and are easy to install. Constructed of quality 316L domestic stainless steel makes for one tough header with a sleek stylish look.

CMI Merc 500 EFI Replacement E-Top Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. All CMI Elbow Top Systems include water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

Note: All CMI Systems are sold without Tailpipes 

The all polished 6″ taller CMI Special Sweep Sport Tubes are commonly used in custom or staggered installations. Custom Marine Sport Tubes are a superior long tube header designed for both racing or virtually any high-performance application. For big-block applications where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines that generate more than one horsepower per cubic inch of displacement. These particular headers are commonly used in staggered and forward engine applications. 

The all polished CMI Sport Tubes are a superior long tube header designed for both racing or virtually any high-performance application. For big-block applications where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines that generate more than one horsepower per cubic inch of displacement.

The all polished CMI Sport Tubes are a superior long tube header designed for both racing or virtually any high-performance application. For big-block applications where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines that generate more than one horsepower per cubic inch of displacement. This version is leaned for use on staggered engine applications.